1. Field of the Invention
This invention relates to fireplace systems which more efficiently and safely deliver heat to the interior of the edifice in which they are located by heat exchange with air circulated within the building as the air is passed through a confining air plenum and in contact with a firebox forming part of the system.
2. The Prior Art
Since wood is an ancient fuel of man and has been used for milleniums to provide heat and light to the human race, numerous ways have been devised for improving the aesthetic effect of the burning wood, and, more recently, a great variety of attempts have been made to more efficiently recover and utilize the thermal energy developed by the wood during burning. The term "recent," of course, in the context of the discussion of man's use of wood for heat and light, encompasses at least the last one or two centuries. The quest for improved ways of recovering the heat energy from burning wood has been intensified yet more recently as a result of the projected depletion of fossil fuel supplies, and particularly, natural gas and petroleum.
Endeavors have been made to retain and permit enjoyment of the aesthetic experience of a blazing wood fire in an open fireplace before which the occupants of a home may sit, while gaining more efficient heating of the home. In so doing, various proposals have been advanced for recapturing from the hot combustion gases developed as the wood burns, a larger portion of the thermal energy in such gases prior to the time that they are vented to the atmosphere through the chimney or flue, and the residual energy contained therein is lost. For many decades now, the concept of taking a portion of the air inside the house, drawing it across the heated external surfaces of the firebox, and then returning it to one or more locations in the house has been in the minds of men, and has been accomplished through various physical structures. In probably the most simple of these, and one still in use, air returns are provided at a location near the bottom of the firebox, and frequently on opposite sides thereof, and this air is then permitted to pass, through natural circulation and the ascendant characteristic of hot air, upwardly around the sides of the firebox and then out through one or more vents located near the top of the firebox, and opening into the same room from which the air is initially extracted. While this arrangement probably recovers a small portion of the heat which would otherwise be carried out through the flue with the combustion gases, the percentage of recovery is not large, and such systems do nothing towards providing heat to the remainder of the house other than the room in which the fireplace is located.
A number of variations on the concept of providing air returns adjacent the firebox and then conveying air in heat exchange relation to the firebox and passing it to one or more locations in the house have been proposed, and some of these have been utilized. One of the older U.S. patents which proposes to provide an air plenum around the firebox for purposes of heat exchange and recovery of a portion of the thermal energy from the hot stack gases is Coulter U.S. Pat. No. 192,416. More recently, Glover U.S. Pat. No. 3,384,619 describes a system which includes, in combination, a fireplace and a forced air conventional central furnace system. The fan or blower of the conventional central heating system is used for circulating air heated by the fireplace at a time when the fireplace is in use. If the temperature drops below an established thermostat setting, the furnace is activated to further heat the circulated air.
Other systems which have proposed to pass the return air within the home or building in close proximity to the firebox, followed by recirculation of the heated air, include U.S. Pat. Nos. 2,791,213; 2,393,812; 4,015,581; 4,206,264; 3,976,047; 3,999,535, and 3,085,564. In the latter two patents, the heated air is connected into a system which integrates the central heating system of the edifice for use when the fireplace is not employed.
In addition to the foregoing and numerous other patented and unpatented proposals for circulating the air into heat exchange proximity to the firebox of the fireplace for purposes of more efficiently burning and utilizing wood, a number of proposals have been advanced, and many patented, for controlling the rate of combustion so as to enhance or at least more closely control the temperature at which the wood is burned in the fireplace, and the time over which it is consumed. In this regard, the manner in which combustion air is introduced to the burning wood has been variously altered, with one proposal being to bring outside air into the firebox at a location beneath or to the rear of the wood, with a dampering system used to control the flow of outside air thus admitted. This has the advantage of providing a source of draft air of low carbon dioxide content without drawing the warm air from the interior of the house for purposes of combustion with subsequent heat loss through the stack or flue. Patents which generally illustrate or describe this type of combustion air source include U.S. Pat. Nos. 2,343,812; 2,409,731; 4,026,263; 3,981,292, and 3,926,174.
Frequently, in conjunction with controlled combustion air drawn from either outside or inside the house, a dampering effect and prevention of internal air loss will be accomplished by providing one or more closure means, such as glass doors, which can be closed across the open front of the fireplace to prevent the air within the room into which the fireplace opens from passing freely up the chimney. The doors also prevent the occurance of excessive draft which will result in too rapid consumption of the wood and excessive heat loss. Such glass doors often are utilized in pairs which open in opposite directions to expose the mouth or open interior of the fireplace. Typical patents illustrative of this construction include U.S. Pat. Nos. 4,026,264; 4,015,581; 3,965,886; 4,004,731; 3,976,047, and 3,976,048.